Analysis On Deformation Law And Stability Of Prestressed Anchor Composite Soil Nailing

More and more deep foundation pit engineering appears in recent years, as the geological conditions of deep foundation pit is complex and the restriction of surrounding environment, single support form has not been able to meet the needs of practical engineering, composite soil nailing technology has become a trend which has been extended and developed based on soil nailing technology. At present, the study on deformation characteristics and stability of composite soil nailing is still less. For that reason, this paper relied on the foundation pit engineering of Changsha Public Security Bureau, High tech District Branch as engineering background, gave numerical simulation of prestressed anchor composite soil nailing, analysed and studied the deformation law and stability of foundation pit during the process of excavation and support. The main research contents and conclusions of this paper are as follows:1. Participated in the work of foundation pit monitoring, collected and analyzed the the monitoring data, the results showed that: the horizontal displacement of top has decreased in a period of time after the anchor has been prestressed; The deformation of monitoring points located in the positive corner of foundation pit was larger; After anchor has been stretched and locked, the axial force roughly characterized by rapid decline, continued to increase, remained stable three stages.2. Gave numerical simulation of prestressed anchor composite soil nailing in two-dimensional, analysed the situation of deformation and structure stress. The results showed that: The horizontal displacement of foundation pit wall along the depth direction presents "drum belly" type distribution, after the completion of excavation, the maximum horizontal displacement occurred in the lower position of foundation pit; The surface settlement of foundation pit along the pit horizontal direction presents "saddle" type distribution, the maximum subsidence occurred in certain position from the foundation pit rather than near the foundation pit; The minimum bottom uplift of foundation pit occurred in the pit wall, the maximum occurred in the center of foundation pit; The axial force of anchorage section along the length direction of anchor presents curved attenuation trend, the maximum occurred in the head position, the minimum occurred in the end position. The distribution of soil nail axial force along the length direction roughly characterized by "the middle is big, two small head", and the maximum axial force point moving backwards along the length direction as excavation proceeds.3. Analysed the stability of each excavation step by using strength reduction fem, and compared with the results calculated by relimit equilibrium method. The results showed that: The results of the two different methods are roughly matched, using strength reduction fem can evaluate the stability of foundation pit well. The potential slip surface of the foundation pit supported by prestressed anchor composite soil nailing is roughly "Circular" shape, and the slip surface deviates from the pit wall to internal of the soil after the wall.4. Analysed the changes of pit wall horizontal displacement, ground surface settlement, foundation pit bottom uplift and axis force of soil nailing, and compared with composite soil nailing, the results showed that the prestressed anchor composite soil nailing structure are more conducive to improve the stability of the foundation pit. Analysed the effect of bolt parameters on deformation of foundation pit, the results showed that the function of deformation control is finite as the anchor length and prestress increased.